Such a roll typically has a plurality of measuring sites integrated into the roll surface and distributed along the roll length at different axial positions for measuring the strip tension, and the measuring sites each have one measuring body flush with the roll surface and carried on one or a plurality of force-measuring sensors.
The flatness-measuring roll detects flatness defects in strips, particularly metal strips, by measuring the distribution of strip tension over the strip width, that is transversely to the strip-travel direction. The entire width of the tensioned strip wraps the flatness-measuring roll at a specified wrap angle and, in doing so, exerts with respect to the local longitudinal tension distribution in the direction of the strip width local contact forces radially inward onto the flatness measurement roll, from which the distribution of strip tension can be detected. Strip defects and, in particular, ripples and strip sabers can then be directly determined from the distribution of strip tension over the strip width because length deviations of individual strip sections are represented by tension differences.
The measuring units at the individual measuring sites have covers that act upon the force-measuring sensors, for example, piezoelectric crystals, situated underneath these covers. Here, it is appropriate to brace the covers against the roll by interposing the piezoelectric quartz. In order to minimize a force transmission between the measuring bodies or the covers on the one hand and the roll body on the other, the measuring bodies or the covers are decoupled from the roll surface by a fully surrounding gap and are exclusively braced against the force sensors, without having further contact with the roll. The measuring bodies or covers are completely and without any noteworthy deformation of the cover subsequently moved against the force-measuring sensors when stressed.
Such measuring rolls are, for example, known from U.S. Pat. No. 5,629,487 or U.S. Pat. No. 7,357,022.
In the flatness-measuring roll known from above-cited U.S. Pat. No. 5,629,487 the measuring bodies are annular covers that each rest on a respective load cell. A plurality of such measuring sites are distributed over the strip width so that the individual measuring sites detect the strip tension for different axial positions. Here, the measuring sites are distributed not only over the strip width but also angularly around the roll. Each measuring site enables making a measurement during each rotation.
DE 10 2004 008 303 disclosed a flatness-measuring roll that has, in the roll surface, flatness sensor bars integrated as measuring bodies, supported on the sensors, and extending obliquely to the roll axis and to the strip-travel direction for determining the tension distribution over the strip width so that such a sensor bar extends over a specified width area on the one hand and over a specified angular extent of the roll area on the other. Such a sensor bar obliquely situated to the roll axis makes it possible to take a plurality of time successive measurements for respective different axial positions of the roll and, for this reason, also of the strip, so that one measuring body (namely one sensor bar) can carry out measurements at different axial positions. Here, normally a plurality of such flatness sensor bars are distributed over the strip width and each cover a specific width range of the measuring roll or of the metal strip.
The known flatness-measuring rolls have generally been proven successful; however, they can be further developed, namely, in particular, with regard to the measuring accuracy.
Furthermore, a flatness-measuring roll is known from DE 41 35 614 in which the force-measuring sensor is covered by a bridge angularly on the roll and, here, is directly fixed on both sides by screw bolts in the cross section of the deflection roll so that during measurement a deformation of the bridge has to occur.
Similarly, a measuring roll is known from U.S. Pat. No. 8,814,076 in which the measuring site arrangements are suspended in the recesses of the roll.